HAWAII (KHNL) - The Big Island Fire Department continued the search for a single-engine plane Friday, missing since Tuesday morning. There are still no signs of the Cessna, or its pilot and two passengers. The U.S Coast Guard had been the lead agency from the beginning, but Thursday night it called off its search.

It was a tough call, something Coast Guard officials agonized over for hours before deciding to suspend the search. They devoted every possible resource into this effort.

It's a search as far and wide as the Big Island of Hawaii itself. The U.S. Coast Guard leads the effort to find a missing single-engine Cessna 172 and its three occupants.

"We covered ten thousand square miles, over 35 separate flights and we started since we got the call. We're up in the air searching," said Petty Officer Luke Clayton, a spokesperson for the U.S. Coast Guard.

Since Tuesday, the Coast Guard combed through the southeast portion of the island. After three days without a sign of veteran pilot Katsuhiro Takahashi and his two passengers, they called off the search Thursday night.

"It's hard to be a professional and this is what you do every day and I joined the Coast Guard just to do this to save people, to help people," said Clayton. "And it's extremely frustrating for us to not come up with anything."

They used technological advancements to help them in the search, like night vision goggles.

"We also have what's called the 'white heat' camera and you're able to see better at night time and you're able to pick up reflective materials," said Clayton.

The dense Kau Forest Reserve hindered search efforts.

"It's pretty much visually hard and with fog and non-cooperating weather, that makes it even harder," said Clayton.

The Hawaii County Fire Department and Island Hopper, the owner of the missing plane, continued the search Friday, but still no luck.

"The case is suspended but if any new details come in, if we pick up radio transmission, or anything like that, we can jump right back into it," said Clayton. "We're standing by 24/7 just in case."

A device that would have helped in the search effort is an "emergency locator transmitter" or an ELT, required on all aircraft. It transmits an audio signal.

If the signal can be heard, rescue agencies can locate the aircraft by the strength and direction of that signal. Island Hoppers says the ELT of the missing Cessna 172 single-engine airplane was working, but it hasn't been heard.

"The fact that the ELT has not been heard is discouraging because it indicates the airplane itself may be in a position such that the signal is being radiated back into the ground rather than up into the sky where it would be easier to find," said Mac Smith, a pilot for 34 years and a veteran flight instructor at Flight School Hawaii. "The fact that they haven't been able to pick up the ELT also tells me that unfortunately people are not able to get to the ELT in the aircraft and move it to a position and move it to a position where it can be heard."

Veteran pilots say the Cessna is generally easy to control and maneuver. In an emergency situation, the challenge is finding a flat area to land the plane safely.